There are indications from Miner's studies in the frog (1956) that information from skin helps bring about the development of "local sign" in reflex responses to stimulation of skin; local sign describes the orienting of a response to the region of the body from which the sensory information is signalled. Our Pilot Study describes a novel spinal reflex in the rat; this is the response to a cutaneous sensory input of a vast skeletal muscle that lies within the skin covering the back and sides of the animal. This reflex shows local sign that is bilaterally represented - stimulation of a localized region of dorsal skin, or of the sensory nerve supplying it, evokes a contraction of "skin" that is focused at the corresponding regions on both sides of the mid-line. However, although the sensory nerves that evoke the reflex are segmental, and its local sign is segmentally expressed, the motor nerves to the muscle all originate in a circumscribed region of the rostral cord. From measurements of the distribution, size and latency of the E.M.G., the expression of local sign in this reflex can be described quantitatively. We now propose to study changes in local sign that may develop after experimentally manipulating peripheral nerve fields in neonatal animals when the CNS is still developing. Subsequent alteration in local sign would indicate that adaptive changes had occurred in the spinal circuitry involved in the reflex, i.e., that a functional "re-wiring" had been induced in the CNS by information from the periphery. The motor and sensory fields are experimentally altered by the redirection of nerves that are regenerating after section, and by the sprouting of intact nerves evoked by the partial denervation of skin and of muscle. We have mapped the innervation and reinnervation patterns of the skin electrophysiologically; the innervation pattern of the muscle, and the location and organization of its motoneurons, will be determined both by electrophysiological and morphological techniques. If central "plasticity" is revealed, we should be able to locate, by these techniques, approximately where in the cord the changes are most likely to have occurred.